Magnetic sensors using the giant magnetoresistive (xe2x80x9cGMRxe2x80x9d) effect, frequently referred to as xe2x80x9cspin valvexe2x80x9d sensors, are known in the art. Spin valve structures are of major interest due to their high magnetoresistive signal and high sensitivity at low fields, which makes them a good candidate for the read sensors of magnetic heads for ultra-high density magnetic recording.
To improve the fabrication of GMR heads for high density recording applications, such as applications greater than 50 Gb/in2, manufacturers look for ways to improve sensitivity, reliability, and the production yields of functional GMR heads. Similarly, it is desirable to fabricate ultra-sensitive GMR heads that can provide a large enough output signal via the moderate sense current scheme to increase the track density significantly.
The reliability of the GMR xe2x80x9cspin-valvexe2x80x9d heads can be affected when the antiferromagnetic pinning layer becomes magnetically inverted, which switches the pulse polarity and degrades the performance of the heads. The readback signal of the GMR sensors can be strongly influenced by the antiferromagnetic orientation, which can cause the disturbed reader to show poor asymmetry, degraded sensitivity, and increased noise. While this failure mode may not be as dramatic as a head crash, it may nonetheless be fatal to the drive.
The stabilization of the pinned layer in a direction perpendicular to the air bearing surface (xe2x80x9cABSxe2x80x9d) of the magnetic head can be critical for optimizing the output reading signal through the use of the GMR effect in spin valve based structures. Presently there exist two types of spin valve structures: the traditional antiferromagnetic pinning spin valve structure and the synthetic antiferromagnetic spin valve structure.
The traditional pinning spin valve structure makes use of multilayer structures with an antiferromagnetic pinning layer. In this technique, there is a direct exchange interaction between the antiferromagnet and the ferromagnetic pinned layer. A number of spin valve heads with different antiferromagnetic pinning layers (such as FeMn, IrMn, FeMnRh, InMn, RhMn, RuMn, NiMn, PtMn, PdPtMn, CrPdMn, and NiO) can be used.
The most prevalent antiferromagnetic pinning layer choices are presently PtMn, IrMn, and CrPbMn, with blocking temperatures between the range of approximately 200 and 380xc2x0 C. NiMn generally has a blocking temperature of at least 330xc2x0 C. or above, but requires long annealing times at relatively high temperature.
Traditional antiferromagnetic pinning spin valve heads can have the following drawbacks. Most of the antiferromagnet/ferromagnet pairs can have blocking temperatures between approximately 150 and 350xc2x0 C. The magnitude of the direct exchange starts to suffer a severe reduction when the temperature is above 200xc2x0 C. In this situation, the magnetic moments of adjacent atomic layers can begin to rotate one from another. The film then starts to lose its antiferromagnetic properties. When the temperature cools again, the atomic layers can realign in the antiparallel fashion, with the fundamental axis in any arbitrary direction. Consequently, a practical reliability problem may arise from the misorientation of the antiferromagnetic magnetic pinning field that can occur spontaneously or because of heating from electrical overstress, thermal asperities, or other external influences. More precisely, heat, together with the magnetic field from the sense current, can invert the magnetization of the antiferromagnetic film. To further complicate matters, while blocking temperatures are usually known for bulk materials or thick films, they differ for each device and within each device. The distribution of the blocking temperature can depend on the fine details of geometry, deposition, and stoichiometry. In most of cases, devices obtained from the same wafer can display a range of blocking temperatures. Therefore, it presents a daunting process-control challenge to magnetic head manufacturers because magnetically stable, single-domain magnetoresistive stacks need to be achieved in a high-volume production setting.
Furthermore, in these spin valve structures, the corrosion problem is not necessarily fully solved. In addition, the pinned layer can tend to rotate its magnetization from the transversal to the longitudinal direction due to strong demagnetizing field. This is another serious and unique problem for reliability issues. In this case, the AF/Co/Permalloy structure could become unstable and be induced to rotate its magnetization especially as the GMR sensor physical dimensions are further reduced.
Another undesirable problem is that the magnetostatic field arising from the pinned layer causes the magnetization of the free layer to be canted with respect to the horizontal direction. The canted magnetization in the free layer can yield amplitude asymmetry and limit head dynamic range. Although using sense current field can counter balance the magnetostatic field, the high density current, nonetheless, can often result in destabilizing the magnetization configuration in the pinned layer, and then reducing pinning field.
It can also be difficult to improve the yield, the reliability, and the PW50 (which is the isolated pulse width at 50% maximum and is proportional to the signal noise ratio) of the dual GMR strips with two anti-ferromagnetic pinning layers. Similarly, it can be difficult to reduce the thickness of AF pinning spin valve heads to further meet the requirement of high recording density applications.
A second type of spin valve structure is based on an alternative pinning mechanism known as the synthetic antiferromagnet (xe2x80x9cSAFxe2x80x9d) technique, which can be used to overcome the non-zero bias field difficulty. A SAF structure consists of two ferromagnetic layers separated by a thin non-magnetic metallic layer, with a strong interlayer exchange coupling, such as a Co/Ru/Co system. When the Ru layer thickness is around 6 xc3x85, the interlayer exchange coupling is antiferromagnetic in nature and the exchange constant can be as large as 1 erg/cm2. This type of SAF based spin valve head can show an enhanced magnetic and thermal stability, and can overcome the non-zero biasing field problem observed in traditional antiferromagnetic pinning spin-valve devices. The SAF based dual strip, however, does require two thick AF pining layers. Thus, this type of spin-valve head structures can still face some issues, such as magnetization stabilization and poor PW50, which can be exacerbated by its multi-layer structure. Designs of dual spin valve strips with synthetic antiferromagnets can contain as many as eleven layers in the GMR stacks, which can also impose a stringent requirement on the integration process of the GMR spin valve head.
This invention addresses some of these problems.
The present invention provides a method and system for fabricating a dual GMR read head, which possess a pseudo spin valve structure.
In one aspect of this invention a magnetoresistive sensor is presented. The sensor includes a first thick Co-alloy based reference layer with first and second surfaces. The sensor also includes a first spacer layer including a first surface contacting the first surface of the first thick Co-alloy layer and a second surface contacting a first surface of a first free layer. The sensor also includes a second spacer layer including a first surface separated from the second surface of the first free layer and a second surface contacting a first surface of a second thick Co-alloy layer.
The sensor can also include a first Ru layer including a first surface contacting the first surface of the first thick Co-alloy layer and a second surface contacting a first surface of a first thin Co-alloy layer. Additionally, the sensor can include a second Ru layer including a first surface contacting a second surface of the second thick Co-alloy layer and a second surface contacting a first surface of a second thin Co-alloy layer.
The sensor can also include an antiferromagnetic layer including a first surface contacting a second surface of the second thick Co-alloy layer. The thickness of the first and second thick Co-based alloy can be approximately between 30 and 55 xc3x85. The first and second thick Co-based alloy can include a material such as CoFe, CoNiFe, CoCr, CoCrTa, CoPt, Co, FePt, CoXPt, or CoB/Pt. The first and second spacer layers can include a Cu-alloy. The first and second free layer include NiFe.
In another aspect of this invention, the sensor can include an isolating layer including a first surface contacting the second surface of the first free layer and a second surface contacting a first surface of a second free layer. In this aspect, the second free layer includes a second surface contacting the first surface of the second spacer layer. The isolating layer can include TaNi.
In another aspect of this invention, a method of manufacturing a magnetoresistive sensor is presented. The method includes forming a layered structure including a first thick Co-alloy layer including opposing first and second surfaces. A first spacer layer including a first surface contacting the first surface of the first thick Co-alloy layer and a second surface contacting a first surface of a first free layer is also formed. A second spacer layer including a first surface separated from the second surface of the first free layer and a second surface contacting a first surface of a second thick Co-alloy layer is also formed.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Implementations can provide one or more of the following advantages.
The DPSV based head sensor can be used to effectively increase the xcex94R/R of GMR strips while providing at least a 8 nm reduction in the stack thickness, compared with the conventional dual spin valve stacks. The elimination of antiferromagnetic layers and specific adaptation of magnetization configurations in this DPSV can improve the reliabilities of the spin valve head sensors. Furthermore, good working temperatures can be achieved because of the lack of the antiferromagnetic layers.
The proposed design can simplify the fabrication process compared to other dual spin valve head fabrication processes. The DPSV can offer a lot of flexibility in terms of optimizing head sensor structures and physical dimensions (i.e., width, height, and thickness) for all relevant stack films, providing the potential to ultimately achieve the best possible GMR head sensor performance. For example, this design can open an avenue potentially to abandon the bottom pole in current GMR head design practice to drastically reduce the half gap, which can meet the future requirement of reducing PW50 for ultra-high density recording. More precisely, two thick Co-based alloy layers could also serve the role of shielding noise from media.